An experimental investigation of the debris flow surge phenomenon : a thesis submitted in partial fulfilment of the requirements for the degree M. App. Sci. [i.e. Master of Applied Science] in Natural Resources Engineering at Lincoln University

Abstract

A review of theoretical, experimental and field work on debris flow surges was undertaken. A new hypothesis concerning the nature of debris flow surges was proposed and tested in the laboratory. The hypothesis is that a debris flow surge can be analytically explained by what was termed a "moving shearing granular dam (MSGD)" model. It proposes that any surge can, in principle, be analyzed macroscopically without knowing the internal details of individual grain motions using a physical description involving three essential forces on the surge head/body. These forces are; an upslope internal frictional force, a downslope gravity force and a downslope hydrostatic force. The quantitative testing was carried out in a 9m long by 150 mm wide flume with transparent walls flume. Quasi-steady state coal grain (diameters up to about 4mm) and wall paper paste surges were produced which propagated down the flume. During these runs an unsaturated region, termed the “wetting front,” was observed within the surge front. Field evidence for the wetting front was established from measurements made on debris flow deposits at Bullock Creek, North Canterbury. The results of the analyses of several runs were found to be consistent with the observed quasi-steady surge front translational motion. Several observations from the literature review of debris flow surge field behaviour are consistent with the central concept underlying the MSGD hypothesis while no observations were found which appear to conflict with the idea.